Device for measuring cloud height

Abstract

A ceilometer operating according to a gating method integrates output signals from a light receiver. The output signals are passed by analog gating means during consecutive time slots following each other at the transmitter frequency and being phase shifted relative to transmitted light pulses. The phase shift of the time slots is varied stepwise after preset time intervals. Signals integrated during a time interval are digitalized, processed n a microprocessor and stored in a memory according to height values determined by respective phase shifts of the time slots. The micro-processors forms a smooth function of the signals accordint to height values, differentiates the smooth function, computes maxima and minima, determines maxima differing from a preset threshold value, and selects a maximum which with increasing height value is followed by a minimum. Then the smooth function is modified by substituting the function interval corresponding to the maximum/minimum pair by a linear function interval and the modified smooth function is integrated. If the integral of the modified function exceeds a preset constant value, a precipitation warning signal is displayed. If the selected maximum sufficiently exceeds a predetermined noise level, the height corresponding to the maximum is indicated as a cloud height.

What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims: 
     
       1. A ceilometer comprising a transmitter for transmitting light pulses, a receiver including a photodetector for receiving light pulses reflected from clouds an generating corresponding output signals, gating means for passing-through the output signals from the receiver during time slots following each other at a transmitter frequency with a predetermined phase shift relative to the transmitted light pulses, an integrator connected to the gating means to integrate the passed output signals over a time interval covering a plurality of time slots of the same phase shift, a memory for storing the integrated signal values in the order of consecutive height values determined by the phase shift of the time slots, evaluation means including means for forming from the stored integrated values a smooth function with respect to a range of consecutive height values,   differentiating means for differentiating the smooth function with respect to the height values,   means for determining from the differentiated smooth function those maxima (F3max) which exceed a predetermined first threshold value and those minima which fall below a predetermined second threshold value and detecting maximum/minimum pairs wherein a minimum immediately follows a maximum, and   indicating means for displaying as cloud heights the values pertaining to maxima in the maximum/minimum pairs.   
     
     
       2. A ceilometer as defined in claim 1, wherein said evaluating means is a microprocessor including an interface, an input/output unit, and being coupled to said memory. 
     
     
       3. A ceilometer as defined in claim 1, wherein said evaluation means integrates the smooth function (F2) over the height measuring range and delivers a command for displaying in said indicating means a precipitation indicating message provided that the integral is greater than a predetermined threshold value. 
     
     
       4. A ceilometer as defined in claim 3, wherein said transmitter and said receiver includes respectively optical devices having surfaces through which the transmitted or received light pulses pass; a blower for blowing air on said optical surfaces; and means for turning on said blower in response to a command issued by said evaluating means in the event that the precipitation indicating message is present. 
     
     
       5. A ceilometer as defined in claim 4, comprising an auxiliary photodetector for detecting reflections from said transmitter optical device caused by soiling of its optical surface, said auxiliary photodetector being coupled to said evaluating means and the latter being programmed so as to issue in the event that the signal from the auxiliary photodetector exceeds a predetermined threshold value, a command for displaying on said indicating means the soiled condition of said optical surfaces. 
     
     
       6. A ceilometer as defined in claim 5, wherein said evaluating means is programmed for blocking said message about the soiling condition of said optical surfaces provided that a command for indicating the precipitation is issued. 
     
     
       7. A ceilometer as defined in claim 4, further comprising means for heating said optical surfaces, and a temperature sensor coupled via said evaluating means to said heating means to activate the same when a freezing temperature is detected. 
     
     
       8. A ceilometer comprising a transmitter for transmitting light pulses, a receiver including a photodetector for receiving light pulses reflected from clouds and generating corresponding output signals, gating means for passing-through the output signals from the receiver during time slots following each other at a transmitter frequency with a predetermined phase shift relative to the transmitted light pulses, an integrator connected to the gating means to integrate the passed output signals over a time interval covering a plurality of time slots of the same phase shift, a memory for storing the integrated signal values (F1) in the order of consecutive height values determined by the phase shift of the time slots, evaluation means including means for forming from the stored integrated values a smooth function (F2) with respect to a range of consecutive height values, means for differentiating the smooth function (F2) with respect to the height values,   means for determining from the differentiated smooth function (F3) those maxima (F3max) which exceed a predetermined first threshold value (C1) and those minima (F3min) which fall below a predetermined second threshold value (C2) and detecting maximum/minimum pairs (F3max/F3min) wherein a minimum (F3min) immediately follows a maximum (F3max),   comparing means for comparing the integrated signal values (F1) with a predetermined third threshold value (C5) and for determining each of those height values which pertains both, to one of the maxima (F3max) in the maximum/minimum pairs (F3max/F3min) and to one of the integrated signal values (F1) exceeding said predetermined third threshold value (C5).   
     
     
       9. A ceilometer comprising a transmitter for transmitting light pulses, a receiver including a photodetector for receiving light pulses reflected from clouds and generating corresponding output signals, gating means for passing-through the output signals from the receiver during time slots following each other at a transmitter frequency with a predetermined phase shift relative to the transmitted light pulses, an integrator connected to the gating means to integrate the passed output signals over a time interval covering a plurality of time slots of the same phase shift, a memory for storing the integrated signal values (F1) in the order of consecutive height values determined by the phase shift of the time slots, evaluation means including means for forming from the stored integrated values a smooth function (F2) with respect to a range of consecutive height values,   differentiating means for differentiating the smooth function (F2) with respect to the height values,   means for determining from the differentiated smooth function F3) those maxima (F3max) which exceed a predetermined first threshold value (C1) and those minima (F3min) which fall below a predetermined second threshold value (C2) and detecting maximun/minimum pairs (F3max/F3min) wherein a minimum (F3min) immediately follws a maximum (F3max),   means for determining the height ranges lying between the height value pertaining to the maximum (F3max) and the height value pertaining to the minimum (F3min) of each maximum/minimum pair (F3max/F3min) and for modifying the smooth function (F2) by substituting function intervals which lie in the determined height ranges with linear function intervals,   means for forming an added function (F6=F4+R) by adding to the modified smooth function (F4) with linear function parts a predetermined noise function (R),   comparing means for comparing the integrated signal values (F1) with the values of the added function (F6=F4+R) related to corresponding height values and for determining each of those height values which pertains both, to one of the maxima (F3max) in the maximum/minimum pairs (F3max/F3min) and to one of the integrated signal values (F1) exceeding the value of the added function (F6=F4+R),   and indicating means for displaying as cloud heights the height values pertaining both to maxima (F3max) in the maximum/minimum pairs (F3max/F3min) and to integrated signal values (F1) exceeding the value of the added function (F6=F4+R).   
     
     
       10. A ceilometer as defined in claim 9, wherein said noise function is dependent on height. 
     
     
       11. A ceilometer as defined in claim 9, wherein said evaluation means integrates the modified smooth function (F4) with linear function parts over the height measuring range and delivers a command for displaying in said indicating means a precipitation indicating message provided that the integral is greater than a predetermined threshold value.